An international team of scientists has suggested that changes in Earth’s orbit resulting in warmer conditions played a role in triggering a rapid global warming event 56 million years ago. This event, known as the Paleocene-Eocene Thermal Maximum (PETM), is considered an analogue of modern climate change.
“The Paleocene-Eocene Thermal Maximum is the closest thing in the geologic record to anything we’re experiencing now and what we’re likely to experience in the future with climate change,” said Lee Kump, professor of geosciences. Penn State University. “There is a lot of interest in better solving this history, and our work answers important questions about what caused the event and the extent of carbon emissions.”
The team of scientists studied key samples from a well-preserved PETM record off the coast of Maryland using astrochronology, a method of identifying sedimentary layers based on orbital patterns that occur over long periods of time known as Milankovitch cycles.
They found that the shape, or eccentricity, of Earth’s orbit and the wobble in its rotation, or precession, favor warmer conditions at the onset of the PETM, and that these orbital configurations together may play a role in triggering the event.
“Orbital triggering may have caused the release of carbon that caused several degrees of global warming during the PETM, contrary to the currently more popular interpretation that massive volcanism released the carbon and triggered the event,” said John Leone Kump. Dean of the College of Earth and Mineral Sciences.
The results were published in the journal
“Those rates are close to an order of magnitude slower than the rate of carbon emissions today, so that is cause for some concern,” Kump said. “We are now emitting carbon at a rate that’s 5 to 10 times higher than our estimates of emissions during this geological event that left an indelible imprint on the planet 56 million years ago.”
The scientists conducted a time series analysis of calcium content and magnetic susceptibility found in the cores, which are proxies for changes in orbital cycles, and used that information to estimate the pacing of the PETM.
Earth’s orbit varies in predictable, calculable ways due to gravitational interactions with the sun and other planets in the solar system. These changes impact how much sunlight reaches Earth and its geographic distribution and therefore influence the climate.
“The reason there’s an expression in the geologic record of these orbital changes is because they affect climate,” Kump said. “And that affects how productive marine and terrestrial organisms are, how much rainfall there is, how much erosion there is on the continents, and therefore how much sediment is carried into the ocean environment.”
Erosion from the paleo Potomac and Susquehanna rivers, which at the onset of the PETM may have rivaled the discharge of the Amazon River, carried sediments to the ocean where they were deposited on the continental shelf. This formation, called the Marlboro Clay, is now inland and offers one of the best-preserved examples of the PETM.
“We can develop histories by coring down through the layers of sediment and extracting specific cycles that are creating this story, just like you could extract each note from a song,” Kump said. “Of course, some of the records are distorted and there are gaps — but we can use the same types of statistical methods that are used in apps that can determine what song you are trying to sing. You can sing a song and if you forget half the words and skip a chorus, it will still be able to determine the song, and we can use that same approach to reconstruct these records.”
Reference: “Astrochronology of the Paleocene-Eocene Thermal Maximum on the Atlantic Coastal Plain” by Mingsong Li, Timothy J. Bralower, Lee R. Kump, Jean M. Self-Trail, James C. Zachos, William D. Rush and Marci M. Robinson, 24 September 2022, Nature Communications.
The study was funded by the National Key R&D Program of China and the Heising-Simons Foundation.
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